This invention relates to sliding headstock automatic lathes, and more particularly to a rotary cutter accessory for such lathes.
Sliding headstock automatic lathes conventionally include a collet chuck which grips a workpiece and reciprocates to advance the workpiece past a plurality of tools. The tools are selectively moved laterally into contact with the workpiece to perform machinery operations such as turning. In the past, turning tools conventionally have had edges which remain stationary, i.e. do not rotate, during the turning operation. Such tools in combination with a rotating workpiece turn parts of circular cross-section, but cannot turn parts of square, or other polygonal cross-sections. Normally rods of polygonal cross-section are available only in certain standard sizes above one-eighth inch, except on special order.
It is known in the patented prior art that a lathe equipped with a cutting tool rotating at twice the speed, and in the same direction, as the workpiece can turn a part of square cross-section. Apparently the prior art technique has not been accepted commercially because the prior art devices presented problems for use on Swiss or sliding headstock lathes. It is generally not practical to turn large quantities of long, very slender small parts with non-sliding headstock machines.
One reason for the difficulty in adapting the rotary cutter to a sliding headstock machine arises from the fact that the headstock and the collet, which grips and rotates the workpiece, move longitudinally with respect to the tool, and the tool moves laterally with respect to the collet. Additionally, the collet and rotating tool must be driven from a common drive which positively avoids relative slippage, in order to assure that the ratio of speeds of rotation of the workpiece and the tool is precisely an integer or whole number, such as 2.0. If the ratio of speeds is, for example, 1.99 because of relative slippage, the cutting tool will strike the part at a slightly different point on each revolution and the desired flat surface is not achieved. One approach to solve the problem is found in my above referenced related application where the power to drive the cutting tool is taken directly off the collet by a pulley and belt arrangement in conjunction with a series of gears.